Global warming issues have brought worldwide attention to reduction of flue gas. Flue gas mainly contains carbon dioxide, sulfur oxides and nitrogen oxides, and, particularly, reduction of sulfur dioxide and nitrogen dioxides is urgently required. In order to satisfy the requirement for reduction of flue gas, there is an urgent need for development of an absorbent capable of absorbing and treating flue gas. Particularly, there is a need for a complex flue gas absorbent capable of simultaneously removing carbon dioxide, sulfur dioxide and nitrogen dioxide, as opposed to a conventional absorbent which separately processes different gases, thereby causing increased costs and comparatively low efficiency.
Carbon dioxide, a major component of flue gas, is a greenhouse gas and has a severe influence upon global warming. Increasing use of fossil fuels is increasing the amount of carbon dioxide discharged into the atmosphere. Development of techniques for treating greenhouse gases, arising from the global warming issues, has been vigorously conducted by Japan, the U.S.A., and European countries since the early 1990s. According to the World Energy Congress (WEC), average carbon dioxide emission in electric power generation should be maintained at 0.2 kgC/kWh or less in order to achieve a carbon dioxide level in the air of 550 ppm or less by 2050. However, currently known techniques can only achieve average carbon dioxide emissions of 0.9 kgC/kWh and 0.4 kgC/kWh for coal and natural gas, respectively.
Under these circumstances, techniques for separating and processing carbon dioxide have been developed in many countries, primarily in consideration of improvement in cost efficiency. Additionally, base techniques have been established and data for development of such techniques has also been substantially realized. Examples of widely available absorbents for use in absorption and separation of carbon dioxide include monoethanolamine (MEA), 2-amino-2-methyl-propanol (AMP), methyldiethanolamine (MDEA), and the like. MEA is a primary alkanol amine, which quickly reacts with carbon dioxide and has a rapid absorption rate. However, since 1 mole of MEA can absorb only 0.5 moles of carbon dioxide, MEA has a comparatively small carbon dioxide absorption capacity. MDEA and AMP are a tertiary alkanol and a sterically hindered alkanol amine, respectively. Therefore, MDEA and AMP have greater carbon dioxide absorption capacities than MEA, as reported in several papers, and require less energy than MEA when desorbing carbon dioxide by heat. However, reaction rates of MDEA and AMP with carbon dioxide are low.
In Korea, techniques for treating air pollutants, such as sulfur dioxide and nitrogen oxides, have been developed via substantial investment and long-term studies, as compared with techniques for treating carbon dioxide, and some are domestically practiced or have been transferred to other countries. Therefore, a technical gap in this field between Korea and other leading countries is not so wide, as compared with carbon dioxide treatment techniques. Presumably, the domestic technique for treating air pollutants approaches a level of about 70% or more when compared with leading countries in this field. However, a technical gap between Korea and other leading countries in treating nitrogen oxides and small quantities of heavy metals are considered slightly wide due to lack of core techniques thereof.
As in carbon dioxide, since sulfur dioxide and nitrogen oxides also react with water to form acids, e.g., sulfuric acid and nitric acid, irrespective of low primary solubility in water, sulfur dioxide and nitrogen oxides can effectively react with an amine solution as well being desorbed by heat.
Therefore, there is an urgent need for development of a new complex absorbent for flue gas, which has not only a higher flue gas absorption capacity but also all of the aforementioned merits of the conventional carbon dioxide absorbents, that is, a high absorption rate due to fast reaction with flue gas, in order to solve such global warming issues.